Abstract: The effects of treating solution concentration on the microstructure, growth rate, and microhardness of Al-alloy MAO coatings, which were prepared in individual Na₂SiO₃, NaAlO₂, and (NaPO₃)₆ solutions, were studied, respectively. The experimental results show that (1) the coating consists of the superficial porous layer and the interior compact layer, the coating microstructure is closely related to the treating solution category while the effect of the treating solution concentration on it is unobvious; and (2) the coating growth rate and microhardness increase gradually with the increased treating solution concentration when the concentration is less than 8 g/L, but both the growth rate and the microhardness are fluctuating with the increased solution concentration when the concentration is more than 8 g/L. This phenomenon accords with Albella’s discharge model of impurity center.

Key words: microarc oxidation, microstructure, coating, growth rate, microhardness